[maksjood]

Hi. How is the data, for example velocity, stored in OpenFOAM? I mean in what manner of indexing? If a 3D model is run.

[mprinkey]

The OpenFOAM forum can help you with the specifics, but it (along with all unstructured CFD codes) store velocity (and other field variables) in 1D arrays. For OpenFOAM (FVM), these represent the cell and/or face values. The cells (say) are not in any particular order. In fact, unless you explicitly reorder them, they will be in the same order that your meshing software stored them. Parallel partition and Reverse Cuthill-McKee can reorder/subdivide them for parallel computation and performance improvements.

But the key notion with unstructured CFD is that the index on your array *MEANS NOTHING* relative to cell's position. This is a hard concept for people used to 2D and 3D structured codes where (i+1,j) is the neighbor (i,j). You have to find your neighbors by a neighbor list. The high-level differential operators in OpenFOAM hide all of those neighbor access details from you. Note too that you will need to look up, say, cell centroid location using the same indexing scheme if you need that in your calculations.